IS 7205:1974 is the Indian Standard (BIS) for design and construction of steel railway bridges. This code details the design and construction of steel railway bridges using the Working Stress Method. It specifies requirements for materials, loads (including standard train, wind, seismic loads), permissible stresses, design of structural components, connections (riveting, bolting, welding), fabrication, and erection.
Lays down guidelines for the design and construction of steel railway bridges.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Design Philosophy Basis | Working Stress Method (WSM): σ_actual ≤ σ_allowable, where σ_allowable is a fraction of yield/ultimate stress. | Limit State Design (LSD): Design Action Effect (S_d) ≤ Design Resistance (R_d), using partial safety factors on loads and materials. | EN 1993-2:2005 |
| Typical Permissible Bending Stress (Tension) | 0.60 * fy (where fy is the yield stress of steel, e.g., ~150 N/mm² for steel with fy=250 N/mm²). | Not directly comparable in LSD. At Ultimate Limit State, stress can reach fy/γM0 (where γM0 is typically 1.0 or 1.05). | EN 1993-2:2005 |
| Dynamic Effect (Impact) for Live Load | Calculated as a Coefficient of Dynamic Augment (CDA) based on span length. A typical formula is CDA = 0.15 + 8/(6+L) where L is in meters (from associated IRS codes). | Calculated as an impact percentage of live load, dependent on span length. E.g., for spans > 80 ft, Impact % = (1600/(L-30)) + 10, where L is in feet. | AREMA MRE, Chapter 15 |
| Vertical Deflection Limit (Live Load Only) | Span / 600 (for open-web girders) or Span / 800 (for plate girders). | Span / 640. | AREMA MRE, Chapter 15 |
| Minimum Thickness for Primary Members | 10 mm | 3/8 inch (9.5 mm) | AREMA MRE, Chapter 15 |
| Longitudinal Force (Braking) | Specified as a fraction of the weight of the design train on the span, typically around 15-20%. | Specified as a fixed value per track (e.g., 1000 kN) or a fraction of vertical load (e.g., 20%), whichever is greater. Q_lbk = 20% of vertical train loads up to max 6000 kN. | EN 1991-2:2003 |